A 28-year-old male agricultural worker from Tamil Nadu presents with a 7-day history of fever, severe headache, and myalgia. On examination, he has a temperature of 39.5°C, a maculopapular rash over the trunk and limbs, and a small black eschar with surrounding erythema on his left thigh. His WBC count is 8,500/μL with relative lymphocytosis. Platelet count is 95,000/μL. Liver enzymes are mildly elevated (AST 78 U/L, ALT 65 U/L). What is the most likely diagnosis?